1. Field of the Invention
The present invention relates to a lamp annealing apparatus used for oxidization, nitriding, heat treatment, or the like of a semiconductor wafer and method of manufacturing a semiconductor device.
2. Description of the Related Art
In recent years, a lamp annealing apparatus which can achieve quick heating and cooling has been used in forming an oxide film or a nitride film on a semiconductor wafer. The conventional lamp annealing apparatus is such that the semiconductor wafer installed in a quartz or metal chamber is heated by emitting light of a xenon lamp or the like, a plurality of process gas sources being connected to the chamber as required depending upon treatment steps.
The construction of such a conventional lamp annealing apparatus will be described with reference to FIG. 1, which is a schematic view thereof. The conventional apparatus, as shown in FIG. 1, has a quartz or metal chamber 10 in which a lamp unit 1 including a xenon lamp or the like as a lamp source, a quartz board 11 to partition the lamp unit 1, a support ring 3 for horizontally supporting one semiconductor wafer 2 and a rotating cylinder 4 for carrying the support ring 3 are equipped.
This rotating cylinder 4, which can rotate the semiconductor wafer 2 in the chamber 10, is rotated by a driving mechanism (not shown). The chamber 10 is provided at its inner bottom with a reflector (an aluminum reflecting mirror) 7 for ensuring stability of temperature and further provided with a gas supply line 5 for supplying process gas into the chamber 10 and a gas exhaust line 6 for exhausting treated gas.
In order to prevent clouding of the reflector 7 generated during the heat-treatment, there is provided a rear face gas supply line 8 for belching out rear face gas from the lower portion of the chamber 10 to the rear surface 22 of the semiconductor wafer 2. The rear face gas supply line 8 branches into a plurality of lines which are connected to a plurality of rear face gas supply ports 12, respectively, opening into the reflector 7 in such a manner that the rear face gas belches out through the rear face gas supply ports 12 into the chamber 10.
A plurality of rear face gas exhaust ports 13 for exhausting the rear face gas are opened at a periphery of the surface of the reflector 7 and the rear face gas exhaust ports 13 are connected to rear face gas exhaust lines 9 so as to exhaust the rear face gas from the chamber 10. In order to achieve even distribution of temperature throughout the semiconductor wafer 2, a sensor (not shown) for controlling the temperature is embedded in the rear face gas supply line slightly below the reflector 7.
In case of heating the semiconductor wafer 2 by using the conventional lamp annealing apparatus having such a construction, first, the semiconductor wafer 2 is transferred from an entrance (not shown) into the chamber 10 to be located on the support ring 3. Then, the desired process gas from the gas supply line 5 as well as the rear face gas from the rear face gas supply line 8 are supplied, and the lamp unit 1 illuminates the rotating semiconductor wafer 2 to be heated up to higher temperature.
In this conventional lamp annealing apparatus, the upper surface of the reflector 7 provided for ensuring stability of temperature is occasionally clouded by out-diffusion from the semiconductor wafer 2 during the heat-treatment. Then, in order to prevent generation of such clouding, the nitrogen gas as the rear face gas is belched out from the rear face gas supply port 12 toward the side of the rear surface 22 of the semiconductor wafer 2 so as to blow off the out-diffusion.
The silicon wafer as the semiconductor wafer 2, however, is formed with a thin natural oxide film before the heat-treatment and the natural oxide film reacts with the nitrogen gas as the rear face gas to generate fine particles of silicon oxide. The fine particles of silicon oxide cloud the reflector.
The new problem can be solved effectively by applying a small amount of oxygen gas into the nitrogen gas as the rear face gas. In this case, the amount of oxygen gas must be controlled because the rear face gas occasionally may turn to the side of the front surface 21 of the wafer 2 through a gap around the support ring 3, which results in causing a problem of oxidizing unfavorably an element forming surface of the front surface 21 of the wafer 2 to vary transistor characteristics depending upon amounts of the oxygen gas applied. Therefore, the control of the mix ratio of oxygen gas to nitrogen gas in the rear face gas is important.
In this way, in the conventional lamp annealing apparatus, as disclosed in Japanese Patent Laid-Open No. 2-280319, the rate control has been carried out on the process gas, but not carried out on the rear face gas.
Accordingly, one object of the present invention is to provide an effective lamp annealing apparatus which prevents clouding of the reflector to achieve stability of temperature for the heat-treatment, and prevents the oxidization of the element forming surface of the front surface of the semiconductor wafer.
Another object of the present invention is to provide an effective method of a semiconductor device by using the lamp annealing apparatus mentioned above.
According to one feature of the present invention, there is provided a lamp annealing apparatus, which comprises a chamber, a support member for supporting a semiconductor wafer having a front surface on which semiconductor elements are to be formed and a rear surface, a lamp unit provided at the side of the front surface in the chamber, a reflector for stabilizing temperature provided at the side of the rear surface in the chamber, a first means for supplying a process gas at the side of the front surface in the chamber to treat a process on the front surface of the semiconductor wafer, and a second means for supplying a rear face gas at the side of the rear surface in the chamber to prevent clouding of the surface of the reflector. The rear face gas is a mixture gas which includes a first gas as a main gas and a second gas as a subordinate gas adding to the first gas, and the second means includes a device which mix the first gas and the second gas to become a desired mixture ratio.
According to another feature of the present invention, there is provided a lamp annealing apparatus, which comprises a lamp unit for heating at an upper portion of a chamber, and a reflector for stabilizing temperature at an lower portion of the chamber. In the chamber, process gas is supplied to a side of a front surface having an element forming surface of a semiconductor wafer located on a rotating cylinder in the chamber to be rotated, and rear face gas for preventing cloud of the reflector is supplied to a side of a rear surface of the semiconductor wafer. The process gas and the rear face gas have different compositions to each other.
According to another aspect of the present invention, there is provided a method of manufacturing a semiconductor device which comprises steps of: setting a semiconductor wafer on a supporting member in a chamber, the semiconductor wafer having a front surface on which semiconductor elements are to be formed and a rear surface, the chamber having a lamp unit for heating at an upper portion of a chamber and a reflector for stabilizing temperature at an lower portion of the chamber; supplying process gas to a side of the front surface of the semiconductor wafer and rear face gas for preventing cloud of the surface of the reflector to a side of the rear surface of the semiconductor wafer, the rear gas being nitrogen gas containing a minor mount of oxygen gas; and heating said semiconductor wafer by the lamp unit.
In the apparatus or method mentioned above, the first gas as a main gas of the rear face gas is preferably nitrogen gas and the second gas as a subordinate gas of the rear gas is preferably oxygen gas containing at 20 ppm (parts per million) to 20000 ppm against the nitrogen gas.
Further, the rear face gas is preferably turned around the periphery of the reflector to be exhausted.
Moreover, a plurality of mass flow controllers is preferably arranged in parallel to control the mix ratio of the first and second gas in the rear face gas.
Further, a plurality of mass flow controllers are preferably adjusted to rates on the different order of ppm, and one of the mass flow controllers is for the nitrogen gas and the others are for oxygen gas.
Yet further, nitrogen gas adjusted by a mass flow controller for the nitrogen gas may be mixed with oxygen gas adjusted by one mass flow controller selected from mass flow controllers for the oxygen gas.